There is presently a great need for high temperature reference electrodes which may be used in measuring systems for determining the percentage of dissolved oxygen in high temperature water in the approximate temperature range of 450.degree. F. to 600.degree. F.
Boilermakers, among others, require an accurate measurement of the amount of oxygen or the oxidizing power of the solution in contact with the various corrodible metals comprising the boiler. As an example, light water reactor systems require extreme safety measures because of the potentially catastrophic damage that could be caused by the failure of such a nuclear reactor system. One way for failure to occur in such reactor systems is by way of corrosion of the pipes or tubes conducting high temperature water through the reactor system vessel or steam generator. It is known that corrosion occurs when the concentration of dissolved oxygen in the water of a light water reactor system exceeds 0.2 ppm. Since this level is found in normal city water, light water reactor systems use treated water having dissolved oxygen levels not to exceed 0.2 ppm for boiling water reactor systems and not to exceed 20 ppb for steam generators of pressurized water reactor systems. Oxygen contaminated water may accidentally enter one of the reactor systems. Therefore, a dissolved oxygen measuring system is required which can measure the exact amount of dissolved oxygen in the water of the light water reactor system so that the critical oxygen level may be accurately monitored and controlled.
One of the problems of providing such a dissolved oxygen measuring system has been the unavailability of a reference electrode which would function in a reducing atmosphere at the temperatures, approximately 550.degree. F., at which the water is maintained in the secondary side light water reactor systems. High temperature reference electrodes are known utilizing Silver-Silver Chloride alloys. Such high temperature reference electrodes are satisfactory except in situations where a reducing atmosphere is present, such as is found in a pressurized water reactor system or a fossil reactor system. The hydrogen in the water in the presence of a reducing atmosphere causes the Silver-Silver Chloride material to break down at these elevated temperatures and the reference electrode is no longer Silver-Silver Chloride but becomes through chemical reaction a different material. Thus, it may be seen that the known high temperature reference electrodes are capable of operating only in situations where an oxidizing atmosphere is present and become unstable in a high temperature reducing atmosphere being unable to provide reproducible output signals. In a PhD Thesis submitted by J. B. Lee to Ohio State University in 1978 entitled "Electrochemical Approach to the Corrosion Problems of Several Fe-Ni-Cr Alloys in High Temperature-High Pressure Water," he indicates that a Silver-Silver-Chloride reference electrode used in a reducing atmosphere of high temperature (288.degree. C.) provided an unstable output signal after several hours or a day. At 250.degree. C. the reference electrode was unstable after 4 to 5 days and even at 100.degree. C. the electrode became unstable after 10 days.
From the foregoing we can see that what was needed was a high temperature reference electrode which could operate at temperatures of approximately 550.degree. F. in a reducing atmosphere such as is found in attempting to measure the dissolved oxygen content in water on the secondary side of a pressurized water reactor system.